The present invention relates to data protocols, and in particular command protocols for model trains.
A variety of control systems are used to control model trains. In one system, the power to the track is increased, or decreased, to control the speed and direction of the train. Multiple trains can be controlled by providing different power levels to the different sections of the track having different trains.
In another type of control system, a coded signal is sent along the track, and addressed to the desired train, giving it a speed and direction. The train itself controls its speed by converting the AC voltage on the track into the desired DC motor voltage for the train according to the received instructions. The instructions can also tell the train to turn on or off its lights, horns, etc. U.S. Pat. Nos. 5,441,223 and 5,749,547 issued to Neil Young et al. show such a system.
FIG. 1A is a perspective drawing of an example layout of a conventional model train system allowing the one-way communication of signals from a base unit to a locomotive and other components.
A hand-held remote control unit 12 is used to transmit signals to a base unit 14 and to a power master unit 150 both of which are connected to train tracks 16. Base unit 14 receives power through an AC adapter 18. A separate transformer 20 is connected to track 16 to apply power to the tracks through power master unit 150. Power master unit 150 is used to control the delivery of power to the track 16 and also is used to superimpose DC control signals on the AC power signal upon request by command signals from the hand-held remote control unit 12.
Power master unit 150 modulates AC track power to the track 16 and also superimposes DC control signals on the track to control special effects and locomotive 24′. Locomotive 24′ is, e.g., a standard Lionel locomotive powered by AC track power and receptive to DC control signals for, e.g., sound effects.
455 kHz transmitter 33 of base unit 14 is configured to transmit an outgoing RF signal between the track and earth ground, which generates an electromagnetic field indicated by lines 22 which propagates along the track. This field will pass through a locomotive 24 and will be received by a capacity antenna located inside the locomotive.
FIG. 1B is a simplified schematic drawing of the conventional system shown in FIG. 1A. FIG. 1B shows a cross-sectional view of locomotive 24, which may be, e.g., a standard locomotive retrofitted or designed to carry antenna 26. The signal will then be communicated from antenna 26 to 455 kHz receiver 37 of engine 24. Locomotive 26 further includes a processor 84 in communication with receiver 37 and configured to interpret the received signal.
Returning to FIG. 1A, receipt of control signals is not limited to moving elements of the train set. The electromagnetic field generated by base unit 14 will also propagate along a line 28 to a switch controller 30. Switch controller 30 also has a receiver in it, and will itself transmit control signals to various devices, such as the track switching module 32 or a moving flag 34.
The use of both base unit 14 and power master unit 150 allows operation and control of several types of locomotives on a single track layout. Locomotives 24 which have been retrofitted or designed to carry receiver 26 are receptive to control signals delivered via base unit 14. Standard locomotives 24′ which have not been so retrofitted may be controlled using DC offset signals produced by power master unit 150.
The remote unit can transmit commands wirelessly to base unit 14, power master unit 150, accessories such as accessory 31, and could transmit directly to train engines instead of through the tracks. Such a transmission directly to the train engine could be used for newer engines with a wireless receiver, while older train engines would continue to receive commands through the tracks.
The communication of signals to moveable and stationary components of a model train as described above, offers a number of advantages. However, even more advantages would be conferred by the ability to both send and receive signals from these train set components.
One challenge to implementing such a bi-direction communication strategy is fitting such a scheme within the existing uni-directional communication framework. Specifically, in order to preserve the value and functionality of existing train sets, it is important for any newly-implemented communications protocol to be backwards compatible with the existing protocol.
There are, however, a number of potential obstacles to implementing such a backwards compatible, bi-directional communication protocol. One obstacle relates to the lack of space allocated for return communications.
FIG. 1C plots a waveform for the signal communicated to the locomotive using the existing Lionel Train Master command format. Specifically, the Lionel Train Master command format uses 23 bits to assemble a command. The 23 bits are grouped together as 4 bit nibbles (a nibble is half of an 8 bit byte) and are represented in hexadecimal (hex). The first four nibbles translate directly to the Train Master command set, instructing the train on speed, use of horns, smoke, lights, etc.
The fifth nibble is a unique number used to detect errors, an error code. The error code represents the addition of the first four nibbles without a carry. The following is an example of a Train Master Engine 1 horn command.
00000000100111000101111009C5Trailer (always ones)Engine 1 Horn|command|error |
The three trailing bits at the end of the message are not currently used to communicate data information. The first trailing bit is set to offset any DC bias imparted by the combination of bits in the command. The last two trailing bits are used to fill the time until the next command packet is received.
FIG. 1C shows that the existing Train Master system involves the continuous transmission of command signals, with each such signal communicating data and allowing synchronization between multiple recipients. Specifically, first command signal 100 is transmitted over the cycle T0-T1 between zero cross-over points 102 and 104. Error nibble 106 of first command signal 100 does not indicate a fault for this signal.
Second command signal 110 is transmitted over the cycle T1-T2 between zero cross-over points 104 and 108. Error nibble 116 of second command signal 110 also does not indicate a fault for this signal.
Third command signal 112 is transmitted over the cycle T3-T4 between zero cross-over points 108 and 122. Checksum bit 126 of third command signal 112 indicates a fault for this signal.
As shown in FIG. 1C, there is no provision for pausing this continuous transmission in order to allow the receiving unit to respond. Moreover, such a pause in transmission would disrupt synchronization between the model train elements established and maintained by continuous emission of the command signal by the base unit.
Another potential obstacle to implementation of a backwards-compatible bidirectional communication protocol is the limited number of available commands. Specifically, all commands of the current Train Master system command structure have been allocated to either designate a variety of commands, or to address different trains or other controlled devices on a train set. No new commands are thus available to allow for handshaking and other functions inherent in bidirectional communication protocols.
The National Model Railroad Association (NMRA) is currently in the process of developing a standard for bidirectional communication with model trains. Proposed standard RP-9.3.1, entitled “Decoder Transmission—Electrical”, is incorporated herein by reference for all purposes. This proposed communication standard relies upon a cutout device to create a short interruption in the transmission of signals, within which a response signal may be initiated. While potentially effective, this approach offers some disadvantages, such as requiring installation of a filter on existing analog locomotives to prevent their operation from being adversely affected by the cut-out device.
U.S. Pat. No. 6,539,292 proposes an alternative bi-directional communications protocol for model trains, in which moving elements continuously transmit information. This approach offers the disadvantage of generation of multiple data signals that may interfere with each other and generate noise, which is already a problem in the model train environment. Also, this patent focuses upon communicating with two-rail model train systems, rather than other system types such as those utilizing three-rails.
Therefore, there is a need in the art for a protocol allowing bi-directional communication with model trains that exhibits low noise and which is backwards compatible with existing unidirectional protocols and with legacy analog locomotives.